Co-induction of anaesthesia: the cardiac patient

Cardiac patients pose special problems to the anaesthetist because of their underlying disease and the nature of the corrective surgery. Information about new methods of induction of anaesthesia obtained in fit patients may not be applicable directly to patients with heart disease. More suitable are patients undergoing cardioversion. Titrating intravenous induction agents to response elicited appears to be more important than the agent used, although it is possible to inject too slowly with drugs whose offset of action is by distribution. Anaesthetic agents alone are not sufficient to ablate the response to tracheal intubation, skin incision and sternotomy. Balancing induction of anaesthesia with small doses of opioid can obtund the haemodynamic responses. The effects of a drug used solely for induction of anaesthesia are unlikely to be present at the end of 3 or 4 h of surgery. However, this is not the case with agents used to maintain anaesthesia if early extubation after anaesthesia is practised. Reports of anaesthetic techniques for cardiac surgery tend to give total doses used rather than the timing and dose of the constituent agents. At Papworth Hospital, Cambridge, UK, after opioid premedication, midazolam sedation is used during insertion of some, or all, vascular cannulae. Two main techniques then exist. Either an intravenous or volatile anaesthetic agent is started immediately, supplemented by an opioid and muscle relaxant, or anaesthesia is induced with opioid and relaxant and the anaesthetic agent is begun only after transfer to the operating theatre, just before skin preparation. Either way, the end-point of induction of anaesthesia is difficult to discern in heavily premedicated patients with midazolam sedation.